In the past, to provide printed wiring boards having fine/high-density conductive patterns, developable liquid photo-resist inks have been used. For example, a liquid photo solder resist ink disclosed in Japanese Patent Early Publication No. 61-243869 is developable with a diluted alkali aqueous solution, which includes an ultraviolet curable resin soluble in the diluted alkali aqueous solution, photopolymerization initiator, and an epoxy compound. To obtain developability, a sufficient amount of carboxyl group is introduced.
However, since the epoxy compound is included in the above-described resist ink, thermal curing of the resist ink easily happens during a predrying step according to a reaction with the carboxyl group in the ultraviolet curable resin, so that there is a problem that defects in development or resolution easily occur. Due to this reason, an amount used of the epoxy compound is limited within a narrow range. As a result, effects brought by blending the epoxy compound such as improvements in electrical corrosion resistance and solder heat resistance of the resist film can not be sufficiently exhibited.